Bazedoxifene acetate (1-[4-(2-azepan-1-yl-ethoxy)-benzyl]-2-(4-hydroxy-phenyl)-3-methyl-1H-indol-5-ol acetic acid), having the chemical formula shown below:
belongs to the class of drugs typically referred to as selective estrogen receptor modulators (SERMs). Consistent with its classification, bazedoxifene demonstrates affinity for estrogen receptors (ER) but shows tissue selective estrogenic effects. For example, bazedoxifene acetate demonstrates little or no stimulation of uterine response in preclinical models of uterine stimulation. Conversely, bazedoxifene acetate demonstrates an estrogen agonist-like effect in preventing bone loss and reducing cholesterol in an ovariectomized rat model of osteopenia. In an MCF-7 cell line (human breast cancer cell line), bazedoxifene acetate behaves as an estrogen antagonist. These data demonstrate that bazedoxifene acetate is estrogenic on bone and cardiovascular lipid parameters and antiestrogenic on uterine and mammary tissue and thus has the potential for treating a number of different disease or disease-like states wherein the estrogen receptor is involved.
U.S. Pat. Nos. 5,998,402 and 6,479,535 report the preparation of bazedoxifene acetate and characterize the salt as having a melting point of 174-178° C. The synthetic preparation of bazedoxifene acetate has also appeared in the general literature. See, for example, Miller et al., J. Med. Chem., 2001, 44, 1654-1657, which reports the salt as a crystalline solid having a melting point of 170.5-172.5° C. Further description of the drug's biological activity has appeared in the general literature as well (e.g. Miller, et al. Drugs of the Future, 2002, 27(2), 117-121).
It is well known that the crystalline polymorph form of a particular drug is often an important determinant of the drug's ease of preparation, stability, solubility, storage stability, ease of formulation and in vivo pharmacology. Polymorphic forms occur where the same composition of matter crystallizes in a different lattice arrangement resulting in different thermodynamic properties and stabilities specific to the particular polymorph form. In cases where two or more polymorph substances can be produced, it is desirable to have a method to make both polymorphs in pure form. In deciding which polymorph is preferable, the numerous properties of the polymorphs must be compared and the preferred polymorph chosen based on the many physical property variables. It is entirely possible that one polymorph form can be preferable in some circumstances where certain aspects such as ease of preparation, stability, etc are deemed to be critical. In other situations, a different polymorph maybe preferred for greater solubility and/or superior pharmacokinetics.
Because improved drug formulations, showing, for example, better bioavailability or better stability are consistently sought, there is an ongoing need for new or purer polymorphic forms of existing drug molecules. The crystalline polymorph of bazedoxifene acetate described herein helps meet these and other needs.